In telecommunications systems, the current trend is to use an ATM protocol in the backbone transport network. The ATM protocol is based on a data structure called a "cell". Cells are data packets having a fixed length of 53 octets. Each cell includes a header of 5 octets and a payload of 48 octets. The header is used to direct the cell through the network and the payload is the useful information portion of each packet.
ATM cells are routed through the network using routing information in the cell header. The routing information consists of a Virtual Path Identifier (VPI) and a Virtual Channel Identifier (VCI). The VPI and VCI pair have only local significance on the link between ATM nodes. ATM nodes, which include ATM switches and cross-connect apparatus, use routing tables to map VCI and VPI values received in an incoming cell to outgoing values used to select an outgoing link as a way of routing the associated cell through the ATM node. A Virtual Circuit Link (VCL) is a logical link between two nodes in the ATM network and is identified by a VCI value. A Virtual Path Link (VPL) is a logical link between two nodes in the network and is identified by a VPI value. A Virtual Circuit Connection (VCC) is identified by a Virtual Circuit Connection Identifier (VCCI). The VCC is an end-to-end connection between two nodes in the network and is formed by the concatenation of VCLs.
When real-time connection-oriented traffic is transferred to an ATM transport backbone, a path must be set up through the backbone network to provide a connection over which cells are routed. Each communication request may also be associated with a service characteristic which may guarantee a specific bandwidth to a communication connection. One way to set up a path through the network is to define a VPC between each pair of ingress/egress points in the network. A VPC generally reserves adequate bandwidth to accommodate an anticipated traffic load for a specific communications application. The VPC eliminates most connection setup signaling and processing but tends to waste network resources because the VPC lacks the granularity required for efficient use of the network capacity.
Network capacity can be utilized more efficiently if a Switched Virtual Circuit (SVC) is used for each communication connection. However, it is well known that the signaling involved in setting up an SVC consumes a certain overhead in the network and may cause connection processing delays. For example, when voice traffic is transported over an ATM network, the setup of SVCs is known to sometimes cause unacceptable call setup delays. This problem is particularly acute during peak busy hours when ATM switches may not be able to sustain a peak time call setup rate.
Solutions have been invented to overcome this problem. For example, U.S. Pat. No. 5,719,863 which issued Feb. 17, 1998 to Hummel describes a method and arrangement for fast through-connect of virtual connections in ATM communication systems. Hummel proposes that virtual connections be set up using cells containing call-associated signaling information. The signaling information is communicated using cells defined as administration and maintenance cells. A permanent virtual connection is set up from an originating to a destination ATM communication terminal equipment. Cells containing the signaling information are labelled as administration and maintenance cells. They are transmitted via the permanent virtual connection. Using the permanent virtual connection for setting up SVCs facilitates and accelerates SVC setup. A drawback of this solution is that a certain portion of the network bandwidth is reserved exclusively for signaling and that portion of the network cannot be used for other purposes even when signaling requirements are minimal. A further disadvantage is that SVC setup still takes time and uses resources in every node involved in the connection.